Major: Earth and Environmental Sciences
Academic Affiliation: Public Policy and Biology
Keneni Godana is a rising junior finishing her bachelor’s degree at the University of Illinois at Chicago. She is currently majoring in Earth and Environmental Sciences with a minor in Public Policy and Biology. Her interests include the intersection of diversity and geoscience, fieldwork, and plate tectonics. During RESESS, she worked on monazite data from the Hellroaring Creek Zone using chemical dating to pinpoint metamorphic and deformation events in the area. Growing up in a family that stressed sustainability and a love for nature, the environment has always been and continues to be her main passion.
Using monazite geochronology to constrain timing of deformation within the Hell Roaring Creek Shear Zone, SW Montana
A wide range of tectonic events from the middle Archean to the Paleoproterozoic have shaped Wyoming Craton, including its collision with the Medicine Hat block, resulting in the Big Sky Orogeny (~1.8-1.7 Ga) in southwest Montana. Here, we examine the ductile deformation preserved within the Hell Roaring Creek shear zone (HRCsz), which is a ~2 km wide dextral transpressive amphibolite facies high strain zone within the Northern Madison Range. The structure divides two separate domains: the Bear Basin block and the Moon Lake block. From previous work, it was concluded that the main deformation fabrics in the Bear Basin block and that immediately preceded the shear zone effects developed around 1750-1740 Ma. Our goal was to specifically constrain the time in which the HRCsz formed, using samples directly from the shear zone and the Moon Lake block.
High resolution geochemical and geochronological techniques were used to analyze the monazite grains because they are compositionally zoned and this zoning is linked to the timing in which the domain grew. Backscatter electron images and x-ray maps for relevant elements were collected by electron microprobe to identify monazite domains and areas of interest. We used the Th-U-total Pb method to date the domains.
In the shear zone samples, most of the monazite grains range in age from 1740-1760 Ma, suggesting that the shear zone occurred during the Big Sky Orogeny and developed just after the deformation in the Bear Basin block.